This invention relates generally to solar cell receivers that house solar energy cells mounted for exposure to sunlight and, more particularly, to a liquid cooled linear focus solar cell receiver in which are established separate structures for establishing electrical insulation and thermal conduction.
Solar photovoltaic cells are semiconductor devices producing, when illuminated, a voltage across their output terminals. In linear-focus type receivers, a plurality of solar cells are interconnected to produce a desired voltage required to operate a load or to be stored in a battery. During exposure to sunlight, these cells as well as the receiver structure tend to heat up due to solar energy impinging on each cell. The solar cells are mounted in thermal contact with a heat conductive supporting structure to transmit heat for removal by a circulating fluid charged within a coolant tube in contact with the receiver.
Solar cells tend to have a lower conversion efficiency at higher operating temperatures. Thus, under strong light concentration, impinging on the cells, the electrical output is lower than expected. To function optimally, excellent heat transfer conditions between the cells and their supporting structure must prevail while maintaining electrical insulation therebetween.
In many conventional solar cell receivers, electrical insulation is satisfied by inserting an insulating material between the solar cell circuit and its structural support functioning as a heat sink. Since it is also desirable to remove heat from the solar cells with minimum temperature drop, such prior art receiver designs generally utilize expensive insulating materials such as alumina or beryllia which combine good electrical insulation with moderate thermal conductivity. However, since optical concentrating systems often result in peak fluxes occurring at or near the central region of the cells, the use of such insulating materials in this region results in significant temperature drops, impairing electrical generation efficiency of the cells as well as increasing the likelihood of thermal expansion. In view of different thermal expansion rates between the cells and mounting structure of the receiver, warping between the cells and mounting structure or thermal mismatch between adjacent cells is likely to occur.
Another problem associated with prior art receiver designs is the difficulty in effecting repair or replacement of faulty cells which impair electrical generation performance. This is because the cells are usually hand bonded to their structural support heat sink, requiring removal from the receiver and interruption of the coolant circuit.